The present invention relates to a two-apron drafting unit comprising at least one sliver guide which projects into the wedge-shaped gap of the roller pair which follows the upper and lower deflection guides of the aprons, has a defined distance to the surfaces of the roller pair, can be moved within certain limits in the longitudinal direction of the roller pair, and is arranged on a holding device which is aligned in parallel to the roller pair as well as with respect to the height of the drafting zone plane.
A two-apron drafting unit of this type is prior art on the basis of U.S. Pat. No. 4,051,577. The sliver guide is arranged by means of a rectangular recess with a clearance on all sides on a leaf-spring-type holding device which, on the one side, is fastened to a rail extending in parallel to the drafting unit rollers against which the cradle is supported which forms the lower deflection guide. The alignment of the sliver guide with respect to the lower deflection guide is therefore only indirect and is relatively rough because of the existing clearance with respect to the holding device. Because of the rough play, the mobility in the longitudinal direction of the roller pair also permits a certain jamming of the sliver guide so that, although the parallelism with respect to the roller pair exists to a certain degree, it is still insufficient.
On the basis of the German Utility Model 19 14 021, it is known to arrange the sliver guides on sliding sections of a rod so that the sliver guides can follow the traversing movement of the fiber material. It is left open where the rod is arranged with respect to the lower deflection guide of the bottom aprons.
In the case of high-draft drawing frames, particularly during the direct spinning of drawing frame slivers on ring spinning machines, the sliver guides must be precisely positioned.
It is therefore an object of the invention to avoid tolerance chains between the deflection guides of the apron and the sliver guide and nevertheless permit a traversing movement of the sliver guides.
This object is achieved in that the holding device, which comprises a slideway for the sliver guide, is arranged on a supporting part connected with the lower deflection guide.
As a result of the fact that the holding device has a slideway for the sliver guide, traversing movements are possible without a loss of the parallelism between the sliver guide and the roller pair and thus of the defined distance between the sliver guide and the roller pair. As a result of the fact that, in addition, the holding device is arranged on a support part connected with the lower deflection guide, the sliver guide is aligned directly on that component to which it belongs so that tolerance chains are avoided.
In a further development of the invention, the supporting part is provided with stop faces for the alignment of the upper deflection guide. As a result, the upper deflection guide can also be aligned in parallel to the roller pair and to the lower deflection guide so that a still higher precision is ensured with respect to the guiding of the fiber.
Advantageously, the holding device is a profiled wire on which the sliver guide is arranged in a non-rotatable manner. Although traversing sliding movements are permitted in this manner, tilting movements of the sliver guide are avoided in every direction.
Expediently, in certain preferred embodiments, the profiled wire is inserted into a correspondingly shaped recess of the supporting part. As a result, not only a simple holding of the profiled wire is obtained but it is aligned from the start with respect to the lower deflection guide itself.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.